Plasmonic or metamaterial nanostructures are usually fabricated on rigid substrate i.e. glass, silicon. Optical functionality of such kinds of nanostructures is limited by the planar surface and thus sensitive to the incident angle of light. Over the last ten years, the understanding and broader application implication of metamaterial has been greatly extended. In fact, metamaterial has been proposed for optical cloak, illusion, absorber, negative index materials etc. in which the electromagnetic response could be engineered by scaling the size parameter of the artificial structures. Furthermore, the shape of the metamaterial device is also an important parameter for manipulating the light scattering. For example, optical cloak and hyperlens fabricated with curved structure were used to meet the modulation of anisotropic refractive index. Metamaterial and plasmonic devices on flexible tape, silk, paper and stretchable PDMS substrate have been demonstrated to show unusual optical response. However, most of the reported flexible metamaterial or plasmonic devices work in the Gigahertz, Terahertz, or Far-infrared frequency. For NIR and visible wavelength applications, the feature size of each unit cell has to be scaled down to tens of nanometer. Most of the current optical metamaterial nanostructures were fabricated on rigid substrate such as glass, silicon and they are fabricated using fabrication techniques such as focus ion beam (FIB), e-beam Lithography (EBL), nano-imprint lithography (NIL) and soft interference lithography (SIL). Recently, single layer flexible metamaterial working at visible-NIR wavelength was directly fabricated on PET substrate using EBL. However, the chemical solution used in metal lift-off process needs to be carefully chosen to avoid chemical damages on the flexible substrate. Besides, the curved surface of the PET substrate brings additional difficulty for the focusing of electron in EBL process. Another important progress in this area is realizing large area 3D flexible metamaterial by nanometer printing technique. In Z. C. Chen, N. R. Han, Z. Y. Pan, Y. D. Gong, T. C. Chong, and M. H. Hong, “Tunable resonance enhancement of multi-layer terahertz metamaterials fabricated by parallel laser micro-lens array lithography on flexible substrates,” Opt. Express 1, 151-157 (2011), a stamp is used to transfer nanostructure to target substrate, and the advantage of this fabrication method is that the stamp can be reused for many times. The U.S. Patent Application Publication No. 2010/0301971 describes an exemplary metamaterial comprising a flexible dielectric substrate that is tunable using an electrical control signal to adjust its electromagnetic properties or via the utility of a tunable resonant circuit that includes a phase change material, wherein the resonant frequency of said metamaterial is tunable via modification of said phase change material either via an electrical control signal or by adjusting the composition of said phase change material. Furthermore, in the prior art, the flexible metamaterial fabricated is dependent on the original substrate used.
The objective of the present invention is to provide method and apparatus of fabrication of a multilayer flexible metamaterial using flip chip transfer (FCT) technique. This technique is different from other similar techniques such as metal lift off process, which fabricates the nanostructures directly onto the flexible substrate or nanometer printing technique. It is a solution-free FCT technique using double-side optical adhesive as the intermediate transfer layer and a tri-layer metamaterial nanostructures on a rigid substrate, which can be transferred onto the adhesive first. Then, the thin optical adhesive and the nanostructure can be conformably coated onto flexible substrates, such as the bent PET substrate, paper etc. Thus, the flexible metamaterial can be fabricated independent of the original substrate used. This flexible metamaterial is tunable via physical manipulation of its flexible substrate with no requirement of changing the material composition of the substrate.
Citation or identification of any reference in this section or any other section of this application shall not be construed as an admission that such reference is available as prior art for the present application.